Gyro-stabilized reference point for cameras



Aug. 6, 1940.

I i F. w. LUTZ ETAL GYRO-STABILIZED REFERENCE POINT FOR CAMERAS Filed Jan. 12, 1938 3 Sheets-Sheet l w la/za Aug. 6,1940. F. w. w: ET- AL 2210,090

GYRO-STABILIZED REFERENCE POINT FOR CAMERAS Filed Jan. 12, 1938 3 Sheets-Sheet 2 k INVENTOR 5 z- 1940. F. w. LUTZ ET AL 2210,090

GYRO-STABILIZED REFERENCE POINT FOR CAMERAS Filed Jan. 12, i938 5 Sheets-Sheet 3 Patented Aug. 6,1940

UNITED STATES PATENT OFF'lCE 2,210,090 I GYRO-STABILIZED REFERENCE romr roa CAME RAS

Application January 12, 1938, Serial No. l84,530

s Claims.

This invention relates to aerial cameras and has particular reference to a means for providing a stabilized reference mark on the camera film, in order to register on the photograph the point on the ground vertically beneath the camera at the instant of exposure. When the film is developed this reference mark clearly appears and serves as a datum point for various purposes, such as mapping and the like. In accordance with the present invention, a

gravity-stabilized light projection means is provided for automatically directing a pencil of light on the camera film to register thereon a fiducial or reference mark, which represents the ground point vertically beneath the camera at the instant of exposure.

In a preferred embodiment of the invention, a gyroscope is employed as the stable element for stabilizing the light projection means, which preferably includes an apertured screen or reticule, operative connections between the gyroscope and screenfor stabilizing the latter, a source of light behind the screen for producing a beam of light through the aperture therein, and a suitable lens and reflector means for confining and directing the beam .upon the camera film so that there is photographically registered on the photograph of a selected area of the ground a reference or fiducial mark indicating the point on the ground vertically beneath the camera at the time of exposure.

The reference or fiducial mark may be of any shape determined by the shape of the screen aperture, such as a small cross, and appears 35 plainly on the film negative. Thus, if the camera is level at the time of the exposure, the stabilized fiducial or reference mark is found approximately in the center of the picture. Various modifications of the stabilizing and light projection may m be provided. e

For a more complete understanding of the invention, reference may be had to the accompanying drawings, in which:

Figure 1 illustrates a vertical section through a more or less conventional form of aerial camera equipped with the apparatus of this invention, wherein the stabilizing and light projection means is positioned outside of the camera and the stabilized light pencil directed into the camera through the lens; Fig. 2 is a horizontal section through the upper portion of the gyroscope stabilizing system, as seen along the line 2-2 of Fig. 1;

Fig. 3 illustrates a strip of developed film having On it the stabilized reference or fiducial marl:

indicating the spot vertically beneath the camera when the picture was taken;

Fig. 4 illustrates a modification thereof, also in vertical section, wherein the stabilized pencil is directed on the film from a point between 5 the film and the lens within the camera;

Fig. 5 is a vertical section through a modification in which a reflector encircles the camera lens for directing the stabilized pencil on the film, and

Fig. 6 is a vertical section through another modification.

Referring to Fig. l of the drawings, numeral l0 designates the housing of an aerial camera of Y the Fairchild type, for example, which is suit- 15 ably mounted in the usual way on a universal support for maintenance of a normal vertical position on an aeroplane or other aerial craft, and whichis fitted with a removable film magazine H having .the reels I2 between which the film l3 passes. A pressure plate l4 holds the film l3 fiat against the frame I 5. Upon exposure, the image of the selected area of the ground beneath the camera is projected by lens is upon the film. 25 Formed in or associated with the camera housing I0 is chamber l1. Suspended within the chamber H, for universal movement on a gimbal support l8 mounted on a bracket l9 secured to the wall of the housing, as illustrated in Figs. 1 0 and 2, is a small vertical-axis gyroscope 20, either of the electrically-driven or air-sustained rotor type, depending upon circumstances and requirements. For example, for use with a vacuum-back camera, the use of an airsustained type gyroscope would be indicated. While a gyroscope is preferred, it is to be understood that' under certain conditions other relatively stable elements, such as a pendulum, may be utilized with equal facility.

Secured to or mounted on the upper part of the casing of the gyroscope 20 is a frame 2| carrying the convex opaque screen 22, spaced above the gyroscope and pierced with an aperture of any selected shape, such as the cross 23 shown in Fig. 2, whose geometrical center lies exactly on the vertical axis of the gyroscope 20. Thus, no matter what the-angle or direction of the relative tilt of the gyroscope 20 the center of the aperture 23, i. e., the center of the reticule so formed, is always on the vertical axis of the gyroscope and indicates that axis. The center of curvature of convex screen 22 is the mean center of the gimbal support It, so that the tilt of the gyroscope will not distort the light beam.

housing. or if desired, carried by the frame it a with flexible feed wires leading thereto. To confine its illumination, the lamp 24 is preferably enveloped in a hood 21 having an opening opposite the screen 22. Inasmuch as the light pro- .iection means 24 is outside the shutter 56' of thecamera, illumination of the lamp 24 need not be controlled in accordance, with the shutter operation, since the latter prevents the lig t beam from striking the film.

5 The light rays issuing from the screen 22, aperture 23 or reticule are rendered (parallel and confined into a narrow beam by the lens 28 carried by a tube 29 mounted on frame 2| and posi-' 'tioned on the vertical axis of the gyroscope for movement therewith. The beam is reflected laterally by a 45 total reflector through an open- V ing 3| in the housing wall 32 upon a translucent reflector 33, such as a half-silvered plane mirror, positioned at an angle of 45 in the field of view of the camera opposite the main lens It. The main lens of the camera, whose focal plane is at the film l3, confines and directs the image of the reticule aperture 23 upon the film H3. The

size of the aperture 23 is selected in accordance 30 with the desired size of thereference mark desired on-the film, consideration being given to the reduction afforded by the lens l5.

Since the light in the reticule pencil is more. intense than that encountered in photography, the reference or fiducial mark appearing on the film is always visible. Fig. 3 illustrates a film negative having thereon the fiducial mark 'which indicates the point on the ground vertically beneath the camera at theinstant the picture was taken.

i As such it may be used asl-a datum point from.

so that the lens" is is not used as a part of the registering means, as in the arrangement of Fig.

1. The gyroscope 20, lamp 24, screen 22, lens 28, v: and reflector 30 are arranged and mounted as in Fig. 1, but at a higher level within or alongside the body It! of the camera proper.

' A lens 3,6 having the same focal length as the camera lens l6 directs the horizontally reflected light pencil fro 45 reflector 30 upon a trans 4 lucent reflector 3 ositioned at an angle of 45 to the focal axis of the camera lens IS in the field of view of the camera between the lens I6 and the film l3. The reflector 31 is preferably very thin so as to cause but little refraction of the light directed upon the film by the lens l6 during an exposure. A partially-silvered film of cellulose derivation will serve the purpose. Because the optical system is inside the camera, the lamp 24 is 70 illuminated only when the shutter I6 is tripped, To that end the switch 34 in the circuit of lamp 24 is arranged to be closed by or simultaneously with the operation of the shutter trip lever or key. The distance between the lens 36 and the re- 75 flector 31 plus the distance between the reflector 31 and the film i3 is made equal to the distance between the lens l8 and the film l3, so that the image of the reticule 22 lies in the focal plane of lens l6, as before. This requirement governs the position of the gyroscope.20 and appurtenant tured for the camera lens It so as to encircle it,

and is so positioned that the parallel rays directed laterally thereon by the lens and plane reflector combination 58, 39', are focused on,the film l3 so that the image of the reticule is sharp and clear. The function and operation of this form of the apparatus of this invention is the same as those of Figs. 1 and 4. As in the arrangement of Fig. 4, the lamp 26 is illuminated only when the shutter it, connected to switch 35, is tripped.

' In the arrangement of Fig. 6, the fiducial mark is recorded on the film from the back thereof, so that there are no reflectors in the field of view or in front of the film. The gyroscope 20, apertured screen 26 and lens 28 carried by the gyroscope, lamp 2 5 with switch 34, and i5 reflector 30 are arranged as before, but at a higher level at the side of the camera housing I 9 opposite the film magazine H containing the reels l2 between which the film l3 passes under pressure plate It.

The center of the pressure plate I4 is provided with a relatively large aperture over which the film I3 is stretched with its rear surface exposed through the aperture. Preferably the aperture contains a translucent plate 4| flush.

with the surface of the pressure plate M. Extending vertically upwardly from aperture 60 is a tube 62 having'a lens $3 at its upper end of the same focal length as camera lens IS and hence is spaced from film 13 the same distance as is lens Positioned above lens $2 is a reflector M. interposed between reflector 30 and M is a double prism 45 whose leading face reflects light downwardly, upon its lower face, which reflects the light through the rear face upon the reflector 44, which, in turn, refiectsthe image through lens 43 upon the rear of the film l3. Since the film back is transparent and has the emulsion on its underside, the image of the screen 22 aperture is recorded on the film. As before, switch 34 is preferably connected for actuation by or simultaneously with the shutter trip lever, so that the image of the screen 22 aperture is directed on the film and when the camera film I3 is exposed.

Although the stabilized fiducial or reference mark 35 is thus recorded on the camera film l3 as a record of the ground point vertically beneath the camera at the instant of exposure, the recording of other data from the rea of the film in the same have been illustrated and described herein, it is 1'0 thereby, but is susceptible of changes in form and detail within the scope of the appended claims.

The term film as used herein and in certain of the appended claims comprehends all forms of photosensitive films however applied, whether on a plate, fiexible cellulose derivative strip, or the like.

We claim:

I. In an aerial camera adapted to be mounted on an aeroplane or the like-and arranged for exposure of aphotosensitive film, said film being carried in the camera for movement therewith, the combination of a member movably associated with said camera and adapted to remain in a predetermined position regardless of ,the attitude I of the camera at the instant of exposure of said film, said position being at the top of a vertical line extending from the camera to that point inthe field of view of the camera at the other end of said line, stable means adapted to be movably mounted on said camera, means for mounting said member on said stable means for movement relative to said camera so that said member always remains in said predetermined position, and means adapted to be mounted on said camera and optically arranged relative to said member and said film for projecting an image of said member on said film within the view recording area thereof at the instant of exposure, whereby the developed film which re cords the camera's field of view includes a picture of said image as a reference of that \portion of the view which lies vertically beneath the camera at the instant ofexposure.

2. In an aerial camera adapted to be mounted on an aeroplane or the like and arranged for exposure of a photosensitive film, saidfilm being carried in the camera for movement therewith, the combination of a member movably associated with said camera and adapted to remain in a predetermined position regardless of the attitude of the camera at the instant of exposure of said film, said position being at the 'top of a vertical line extending from the camera to that.point in the field of view of the camera at the other end of said line, a gyroscope adapted to be movably mounted on said camera, means for mounting said member on said gyroscope for movement relative to said camera so that said member always remains in said predetermined position, and means adapted to be mounted. on said camera and optically arranged relative to said member and said film for projecting an image of said member on said film within the view recording area thereof at the instant of exposure, whereby the developed film which records the camera's field of viewincludes a pic- ,ture of said image as a reference of that portion of the. view which lies vertically beneath the camera at the instant of exposure.

3. In an aerial camera. adapted to be mounted on an aeroplane or the like and arranged for exposure of a photosensitive film, said film being carried in the camera for movement therewith, the combination 01 a member movably associated with said camera and adapted to remain in a predetermined'position regardless of .the attitude of the camera at the instant of exposure oi said film, said position being at the top of avertical line extending from the camera to that point in the field of view of the camera -at the other -nd of said line, stable means adapted to be movably mounted on said camera,

I beneath the camera at the instant of exposure.

film, said position being at the top of a vertical mounted on said camera and optically arranged 5 relatie to said member and said film for projecting an image of said member on said film within the view recording area thereof at: the instant of exposure, said image projecting means including an optical system comprising a plural ity of lenses including the camera lens, all of said lenses being mounted on said camera, whereby the developed film which records the cameras field of view includes a picture of said image as a reference of that portion of the view which lies vertically beneath the camera at the instant of exposure.

4. In an aerial camera adapted to be mounted on an aeroplane or the like and arranged for exposure of a photosensitive film, said film being carried in the camera for movement therewith, the combination of a member adapted to be movably associated with said camera and adapted to remain in a predetermined position regardless of the attitude of the camera at the instant% of exposure of said film, said position being at thetop of a vertical line extending from the camera to that point in the field of view of the camera at the other end of said line, said member including an apertured element, stable means adapted to be movably mounted on said camera, means for mounting said member on said stable means for movement relative to said camera so that said member always remains in said predetermined position, a source of light associated with said apertured element, and an optical systeminounted in said camera in operative relationship to said member and to said source of light for projecting an image of the aperture in said element on the film at the instant of exposure thereof, whereby the developed film which records the camerasfield of view includes a picture of said image as a reference of that portion of the view which lies vertically its 5. In an aerial camera adapted to be mounted on an aeroplane or the like and arranged for exposure of a-' photosensitive film, said film being carried in the camera for movement therewith, the combination of a member movably associated with said camera and adapted to remain in a predetermined position regardlessjof the attitude of the camera at the instant of exposure of said line extending from the camera to that point in the field of view of the camera at the other end of said line, stable means adapted to be movably mounted on said camera, means for mounting said member on said stable means for movement relative to said camera so that said member always remains in said predetermined position, means adapted to be mounted on said camera and operatively associated with said member for projecting an image thereof, and an optical system'adapted to be mounted in said camera and including a plurality of reflectors for transmitting I said projected image onto said film, one of said reflectors being positioned substantially in alignment with the camera lens and film but exteriorly of said lens so that the projection of the image passes through the camera lens, whereby the developed film which records the camera's field of view includes a picture of said image as a refer-' ence of that portion of the view which lies verthe combination ofa r'nem tically beneath the camera. at the instant of enposure. 7

6. In an aerial. camera adapted to be mounted on an aeroplane or the like and arranged for exposure of a photosensitive film, said film .being carried in the camera for movement therewith, the combination of a member movably associated with said camera and adapted to remain in a predetermined position regardless of the attitude of relative to said camera so that said member always remains in said predetermined position, and means adapted to be mounted in said camera and including a plurality of lenses and reflectors optically associated with said member for projecting an image thereof on the reverse side of said film at the instant of exposure thereof, one of said refiectors comprising a double prism, whereby the developed which records the camera's field of view includes a picture of said image as a reference of that: portion of the view which lies vertically beneath the camera at the instant of exposure.

7. In an aerial camera adapted to be mounted on an aeroplane or the like and arranged for exposure of a photosensitive film, said film being carried in the camera for m vement therewith, mevably associated with said camera and adapted to remain in a predetermined position regardless of the attitude of the camera at the instant of exposure of said film, said position being at the top of a vertical line extending from the camera to that point in the field of view of the camera at the other end of said line, stable means adapted to be movably means adapted'to be mounted in said camera and operatively associated with said member for creating and projecting an image thereof onto said film at the instant of exposure, said last-mentioned means including a plurality of reflectors,

at least one oi-which is positioned between the camera lens and the film, whereby the developed film which records the cameras field of view includes a picture of said image as a reference of that portion of the view which lies vertically beneath the camera at the instant of exposure.

8. An aerial camera adapted to be mounted on an aeroplane or the like and arranged for exposure of a photosensitive film, said him being carried in the camera for movement therewith, said camera comprising, in combination, a casing adapted to support the film and the camera lens, a gyroscope mounted in said casing, an apertured member, means connecting said apertured member with said gyroscope so that said member moves therewith in relation to the camera, a source of light in said casing andpositioned in relation to the aperture in said member so that a beam of light in the general shape of said aperture is projected therefrom, and an optical system in said casing including a plurality oi reflectors optically arranged with respect to said aperture and to said film so that said beam of light is projected against 'said film, whereby that portion of the film against which said beam 'is projected will have recorded thereon when developed that point of the view photographed which is vertically beneath the camera at the instant of exposure. A.

mICK'W. LUTZ. JO D. PEACE, Ja. 

